The present invention relates to an option unit detecting apparatus for an electronic equipment, and more particularly, to an apparatus for detecting a connecting status of an option unit to an electronic equipment bY rendering a switching element provided in an electronic equipment operative or inoperative depending on whether or not a current can be supplied to a semiconductor device provided in the option unit.
In general, an electronic equipment, such as a personal computer Or an electronic typewriter, is coupled to option units, such as a floppy disk drive or an auto cut-sheet feeder (hereinafter referred to as ACF). so as to permit desired data to be printed on a printing sheet or stored into a storage medium, or permit a printing sheet to be automatically fed. In the electronic typewriter, for example, the connection status of an option unit, such as ACF, is detected to eliminate an operational inconvenience. As shown in FIG. 7, a CPU 32 provided in a controller 31 of connector 39 and has another port P5 coupled through an option-unit detecting signal line 37 to a terminal 42 of the connector 39. A reference voltage terminal E1 is coupled through a power line 35 to a terminal 40 of the connector 39 which has a terminal 43 connected to ground through a ground line 38. The option-unit detecting signal line 37 is coupled through a pull-up resistor R8 to the reference voltage terminal E1, and the drive signal line 36 is also coupled through a pull-up resistor R9 to this terminal El.
Tho control system of an ACF 50 is provided with at least a connector 44, a solenoid 49 for driving an engagement pawl to drive a feed roller for automatic sheer feeding, and an NPN transistor Tr4 for energizing the solenoid 49. A terminal 45 associated with the terminal 40 is coupled to the one end of the solenoid 49, a terminal 46 associated with the terminal 41 is coupled to the base of the transistor Tr4, and terminals 47 and 4B associated respectively with the terminal 42 and 43 are coupled to the emitter of the transistor Tr4.
When the ACF 50 is not coupled to the typewriter 30, a high-level signal is impressed on the port P5 due to the connection to the reference voltage +V, whereas when the ACF 50 is coupled to the typewriter 30, the option-unit detecting signal line 37 is coupled to the ground line 38 through the terminals 42, 47, 48 and 43, and the port P5 is applied with a low-level signal. Accordingly, the presence or absence of the ACF 50 can be detected from the signal level at the port P5.
As described, in order to detect coupling of an option unit 50 to an electronic equipment, four cable lines are required; power line 35, drive signal line 36, option-unit detecting signal line 3A, and ground line 3B. with longer connection cable lines for coupling the typewriter 30 to ACF 50, the manufacturing cost would be increased due to the necessity for separately providing the signal line 37 for detecting the connection status of an option unit. Further, noise is more likely to be generated by an electric wave radiated from the connection cable lines, and the connector 39 would be enlarged in size to thus increase the cost of the cable due to the necessity for separately providing the terminal 42 for the signal line 37 to the connector 39.